Weft feed gripper for looms

Abstract: A weft feed gripper (1) wherein the gripper body (2) terminates with a hook (3), and presents a slider (4) for engaging the weft inside the hook (3), and control means (11) cooperating with a gripper opening element (10) on the loom, for selectively moving the slider between a first position adjacent to the hook and wherein it retains the weft, and a second position wherein the slider is detached from the hook to release the weft. The control means include a flexible leaf spring (19) with a first profile; a flexible strap (12) secured at opposite ends to the slider and the gripper body and mounted so as to slide inside the gripper body; and second profiles (18) on the gripper body; the strap sliding between the profiles, and being deformed elastically when the leaf spring cooperates with and is flexed by the gripper opening element, so as to move the slider between the first and second positions.

Description: The present invention relates to a weft feed gripper for looms, and in particular to a controlled-weft-release drawing gripper. As is known, on modern looms, the weft yarn is inserted inside the shed, formed by the heddles, using a carrying and a drawing gripper, which travel back and forth inside the shed in a crosswise direction to the warp yarns; the carrying gripper picking up the weft yarn from the reel and carrying it roughly halfway along the shed to the so-called "exchange point", and the drawing gripper picking up the yarn from the carrying gripper at the exchange point and drawing it to the end of the shed where it is released from the drawing gripper. Pickup and release of the weft - at least release - are controlled by the interaction of a fixed element or "gripper opener" located along the path of the gripper in question, usually the drawing gripper, and a movable or "pressure" element on the gripper. To enable interaction of the two elements, known grippers, as e.g. that shown in EP-A-0164628, are of complex design and, in particular, feature elements pivoting on the gripper body for interacting with the gripper opener. Due to the high speed - roughly 30 m/sec - at which the gripper opener is contacted, the release mechanism undergoes considerable mechanical shock seriously impairing the reliability of the pivots. In more general terms, as a consequence of the high output demanded of modern looms, opening of the weft feed grippers for pickup/release of the weft yarn is now a critical operation in which the high operating speed and small size of the grippers result in severe stress of the gripper components. Moreover, known opening mechanisms are invariably cumbersome and subject to severe wear. It is an object of the present invention to provide a weft feed gripper opened and closed by means of known "gripper opening" elements but designed to overcome the aforementioned drawbacks, and which in particular features a reliable, straightforward, low-cost, compact opening mechanism. According to the present invention, there is provided a weft feed gripper for looms, comprising a gripper body terminating with a hook at one end; a slider mounted in sliding manner on the gripper body and presenting, towards the hook, a jaw for engaging the weft; and control means cooperating with a gripper opening element on the loom, for selectively moving the slider between a first position, wherein the jaw cooperates with the hook to retain the weft yarn therein, and a second position, wherein the jaw is detached from the hook to release the weft yarn; said cintrol means comprising a flexible strap secured at one end to the slider characterized in that said control means also comprise: first and second pressure means presenting mating profiles and fitted to the gripper body in parted manner and so as to move in relation to each other, the first pressure means cooperating with said gripper opening element so as to move towards the second pressure means; the flexible strap being secured at the opposite end to the gripper body, mounted in sliding manner between said first and second pressure means, and being deformed elastically so as to reproduce said mating profiles when said first and second pressure means are mated; and said mating profiles being so formed as to move the slider between said first and second positions. More specifically, the first pressure means comprise a flexible leaf spring fitted in projecting manner at a first end to the gripper body, and presenting at least a first profiled element at a second end opposite the first and on the face facing said strap and detached from the strap when the leaf spring is undeformed; and the second pressure means comprise at least a pair of second profiled elements mating with the first, integral with the gripper body on the side facing said leaf spring, and between which the first profiled element is accommodated. According to a preferred embodiment, the gripper body and the leaf spring are formed from blanked, bent sheet metal; the strap runs horizontally in contact with the bottom wall of the gripper body; and the profiled elements are formed by semiblanking and bending respective facing portions of the gripper body and the leaf spring, so that the second elements are defined by respective semiblanked curved tabs bent so as to define, beneath the strap, a cavity in which part of the strap is inserted by the first element. As such, the strap is deformed outwards of its plane, and is shortened longitudinally (measured parallel to its direction of travel) in said plane by an amount equal to the shortest path between the profiles of the mated profiled elements, so as to move the slider by the desired amount. The profiled elements may also be tooled in one piece with, or applied to, the leaf spring and the gripper body; and the movement of the slider is counteracted by a helical spring for restoring the gripper to the closed position. Since the strap cooperates in sliding manner with the profiled elements of the pressure means, provision is made for covering the sliding contact surfaces with antifriction material such as RULON or TEFLON (registered trade marks). By virtue of the design of the gripper according to the present invention, the opening mechanism is fully capable of withstanding the mechanical shock caused by the high operating speed of the gripper, and is lightweight, compact, cheap to produce and highly reliable by featuring no pivoting elements and by mainly extending longitudinally, thus enabling fairly small cross sections of the gripper. Moreover, the profiles of the pressure means may be so selected as to form an ample supporting surface between the moving parts for reducing operating pressure and wear. A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a weft feed gripper for looms in accordance with the present invention and in the closed position; Figure 2 shows the Figure 1 gripper in the open position; Figures 3, 4 and 5 show different embodiments of a detail of the gripper in Figures 1 and 2; Figures 6, 7 and 8 show, schematically, further details of the gripper in Figures 1 and 2. Number 1 in Figures 1 and 2 indicates a weft feed gripper for a known loom of which, for the sake of simplicity, is shown only a known gripper opening element 10 which is fixed in relation to gripper 1, is normally located towards the end of the stroke of the gripper, and past which gripper 1 moves back and forth in use. Gripper 1 comprises a gripper body 2 terminating at one end with a hook 3; and a slider 4 mounted in sliding manner on gripper body 2 and presenting, towards hook 3, a jaw 5 for engaging a weft yarn (not shown). Though the example shown relates to a drawing gripper, the following description obviously also applies to a carrying gripper or, in general, to any type of weft feed gripper requiring that it be opened in controlled manner at any point along its path. Gripper 1 also comprises control means indicated as a whole by 11 and cooperating with gripper opening element 10 for selectively moving slider 4 between a first position (Figure 1) wherein gripper 1 is closed and jaw 5 cooperates with hook 3 to retain the weft yarn (not shown) inside the hook, and a second position (Figure 2) wherein gripper 1 is open and jaw 5 is detached from hook 3 to permit release of the weft yarn. According to the present invention, control means 11 comprise a flexible, elastically deformable strap 12 secured at opposite ends 13 and 14 to gripper body 2 and slider 4 respectively; and pressure means 16, 18 presenting mating profiles, and which provide for elastically deforming strap 12 outwards of its plane, are fitted integral with gripper body 2 in parted manner and so as to move in relation to each other, and between which strap 12 is mounted in sliding manner. As shown in Figures 1, 2 and 5, pressure means 16 comprise a flexible leaf spring 19 fitted in projecting manner at one end 20 to gripper body 2, and presenting, at the opposite end 21 and on face 22 facing strap 12, a profiled element 23 having, in the example shown, a cylindrical profile extending from leaf spring 19 towards gripper body 2. Leaf spring 19 is so shaped and fitted that, when it is undeformed, face 22 is detached (Figure 1) from both strap 12 and gripper body 2, and more specifically, in the example shown, from the base wall 25 of gripper body 2 on which strap 12 is mounted. Leaf spring 19 is also shaped, on face 24 opposite face 22, to cooperate with gripper opener 10 and move towards wall 25 (Figure 2) when gripper 1 is moved in the direction of arrow A (Figure 1). In the undeformed position (Figure 1), leaf spring 19 (with the exception of end 20) is positioned obliquely and detached from wall 25, whereas, in the deformed position cooperating with element 10 (Figures 2 and 5), it is positioned substantially parallel and close to wall 25. Facing end 21 of leaf spring 19, wall 25 in turn presents pressure means 18 which comprise at least a pair of profiled elements 26 integral with gripper body 2 and the profiles of which mate longitudinally with that of element 23. Element 23 is so sized and located as to fit between elements 26 (Figures 2 and 5) when leaf spring 19 is flexed towards wall 25, so that strap 12 is gripped between elements 23 and 26 and deformed elastically by them to reproduce their mating profiles. As shown by way of example in Figures 1, 2 and 5, gripper body 2 and leaf spring 19 are formed from appropriately blanked and bent sheet metal, and the portion of leaf spring 19 extending between ends 20 and 21 is so formed, e.g. using spring steel, as to be highly flexible. Gripper body 2 is in the form of a U-section channel, the bottom wall of which is defined by wall 25, and strap 12 is placed on and parallel to wall 25. At end 13, strap 12, together with end 20 of leaf spring 19, is secured to wall 25 by means of one or more common rivets 30, whereas, at the opposite end 14, it is secured solely to slider 4 by a riveted articulated joint 31 sliding together with slider 4 in relation to body 2. In the Figure 5 embodiment, profiled elements 23 and 26 are formed by semiblanking and bending respective facing portions of leaf spring 19 and bottom wall 25 of channel body 2; and, in the example shown, elements 26 are defined by respective curved tabs semiblanked and bent so as to define, beneath strap 12, a cavity 33 into which part of strap 12 is inserted by element 23. In the Figure 4 embodiment, profiled elements 23 and 26 are integral portions of leaf spring 19 and gripper body 2 respectively, with which they are formed, e.g. tooled or pressed, in one piece. In the Figure 3 variation, on the other hand, profiled elements 23 and 26 are formed separately from and fitted to leaf spring 19 and gripper body 2 by fastening means 35, e.g. screws or rivets. In both cases, however, a cavity 33 is formed between elements 26 for receiving the mating element 23 of leaf spring 19. Elements 23 and 26 on either side of flexible strap 12 therefore provide for deforming it outwards of its plane - in the example shown, into cavity 33 between elements 26 - when leaf spring 19 is deformed elastically, and more specifically when leaf spring 19 is flexed towards wall 25 by element 10 as a consequence of the movement of gripper 1. As strap 12 is only secured to wall 25 at point 30, it is therefore free to slide inside body 2 and along bottom wall 25 when deformed. When gripped between elements 23 and 26, therefore, strap 12 is deformed outwards of its plane and into cavity 33 to such an extent as to be shortened longitudinally in said plane, i.e. the plane of wall 25, by an amount equal to the shortest path between profiles P1 of elements 26 and mating profile P of element 23. As such, by simply forming elements 23 and 26 accordingly, it is possible, when leaf spring 19 is flexed as shown in Figure 2, to so deform strap 12 as to shorten it in the plane of wall 25 and bring end 14 towards end 13 by the desired amount. Since slider 4 is secured integral with end 14, deforming strap 12 obviously also provides, according to the invention, for moving slider 4 between the Figure 1 and Figure 2 positions and by exactly the desired amount to open gripper 1. Upon gripper 1 clearing element 10, leaf spring 19 springs back to the undeformed position; element 23 releases strap 12; and, being elastic, strap 12 also springs back to the undeformed position in Figure 1 wherein it is perfectly parallel to wall 25. The springback action of strap 12 is probably sufficient in itself to restore slider 4 to the closed position. Nevertheless, to accelerate closure of gripper 1, ensure firm grip and prevent any possibility of jamming, gripper 1 according to the invention also presents elastic means defined by a helical spring 40 fitted to gripper body 2 and which provides for maintaining slider 4 in the Figure 1 position and elastically counteracting its movement into the Figure 2 position. Spring 40 is packed, for example, between a first shoulder 41 integral with slider 4, and a second shoulder 42 integral with gripper body 2, and is wound about a rod 44 connecting slider 4 to strap 12 downstream from the spring. During operation of gripper 1, a good deal of sliding friction therefore exists between strap 12 and elements 23, 26, which is further aggravated by stress exchanged even perpendicular to the plane of strap 12. The sliding contact surfaces of strap 12 and/or elements 23, 26 are therefore preferably covered (Figure 6) with a protective sheath 50 composed of one or more layers 52 of antifriction material such as PTFE, in particular RULON or TEFLON (registered trade marks), possibly copolymerized with a base material 51 such as polyester or carbon fiber. Alternatively (Figures 7 and 8), flexible strap 12, which is normally made of a thin strip of spring steel, is formed as a sandwich element comprising a flexible core 70 of one or a number of superimposed layers or strips 71 of material which is elastically deformable but resistant to tensile stress, such as steel and/or polyester and/or carbon and/or KEVLAR (registered trade mark), and two opposite surface cover layers 73 made of antifriction material as specified above. Clearly, changes may be made to the gripper as described and illustrated herein without, however, departing from the scope of the present invention. In particular, leaf spring 19 may be provided with a number of profiled elements 23, each mating with a respective pair of elements 26 on gripper body 2, in which case, the gripper opening stroke of slider 4 is obviously increased with no increase in the width of gripper 1 and in particular with no increase in the inflection of leaf spring 19 by element 10. For a given inflection of leaf spring 19, in fact, strap 12 is shortened in its plane and, hence, the stroke of slider 4 increased in proportion to the number of elements 23 provided.

Claims: A weft feed gripper (1) for looms, comprising a gripper body (2) terminating with a hook (3) at one end; a slider (4) mounted in sliding manner on the gripper body and presenting, towards the hook, a jaw (5) for engaging the weft; and control means (11) cooperating with a gripper opening element (10) on the loom, for selectively moving the slider (4) between a first position, wherein the jaw (5) cooperates with the hook (3) to retain the weft yarn therein, and a second position, wherein the jaw (5) is detached from the hook (3) to release the weft yarn; said control means (11) comprising a flexible strap (12) secured at one end to the slider (4) ; characterized in that said control means (11) also comprise: first and second pressure means (16,18) presenting mating profiles and fitted to the gripper body (2) in parted manner and so as to move in relation to each other, the first pressure means (16) cooperating with said gripper opening element (10) so as to move towards the second pressure means (18); the flexible strap (12) being secured at the opposite end to the gripper body (2), mounted in sliding manner between said first and second pressure means (16,18), and being deformed elastically so as to reproduce said mating profiles when said first and second pressure means (16,18) are mated; and said mating profiles being so formed as to move the slider (4) between said first and second positions. A weft feed gripper as claimed in Claim 1, characterized in that said first pressure means (16) comprise a flexible leaf spring (19) fitted in projecting manner at a first end to the gripper body (2), and presenting at least a first profiled element (23) at a second end opposite the first and on the face facing said strap (12) and detached from the strap when the leaf spring (19) is undeformed; the second pressure means (18) comprising at least a pair of second profiled elements (26) mating with the first (23), integral with the gripper body (2) on the side facing said leaf spring (19), and between which the first profiled element (23) is accommodated. A weft feed gripper as claimed in Claim 2, characterized in that said gripper body (2) and said leaf spring (19) are formed from blanked, bent sheet metal; the strap (12) running horizontally in contact with the bottom wall of the gripper body (2); and said profiled elements (23,26) being formed by semiblanking and bending respective facing portions of the gripper body (2) and the leaf spring (19), so that the second elements (26) are defined by respective semiblanked curved tabs bent so as to define, beneath the strap (12), a cavity (33) in which part of the strap (12) is inserted by the first element (23). A weft feed gripper as claimed in Claim 2, characterized in that said profiled elements (23,26) are integral portions of, and formed in one piece with, the leaf spring (19) and gripper body (2). A weft feed gripper as claimed in Claim 2, characterized in that said profiled elements (26,23) are formed separately from, and fitted by fastening means to, the gripper body (2) and the leaf spring (19). A weft feed gripper as claimed in one of the foregoing Claims, characterized in that said control means also comprise elastic means (40) carried on the gripper body (2) and which provide for maintaining the slider (4) in said first position and counteracting the movement of the slider (4) into said second position. A weft feed gripper as claimed in Claim 6, characterized in that said elastic means comprise a helical spring (40) packed between a first shoulder (41) integral with the slider (4) and a second shoulder (42) integral with the gripper body (2), and wound about a rod (44) connecting the slider to the flexible strap (12) downstream from the spring (40). A weft feed gripper as claimed in one of the foregoing Claims, characterized in that the sliding contact surfaces of said strap (12) and/or said pressure means (16,18) are covered with a layer (50;52) of antifriction material, in particular RULON or TEFLON (registered trade marks). A weft feed gripper as claimed in one of the foregoing Claims, characterized in that said flexible strap (12) is in the form of a sandwich element comprising a flexible core (70) of one or a number of superimposed layers or strips (71) of elastically deformable material, and two opposite surface cover layers (73) of antifriction material.

Inventors: BONACINA CARLO, BONACINA, CARLO
Applicants: INTERPATENTS LTD, INTERPATENT LIMITED
Application year: 1994
Main classification: D03D47
IPC codes: D03D47